The present invention relates to a terminal unit for the outlet of conditioned air in a centralized conditioning system.
Units of the above-mentioned kind are well known, which are generally mounted to the celling of a room to be conditioned, completely or partially in view, as there is provided a false ceiling wherefrom they project with their end being the outlet of conditioned air. These terminal units can be divided into two basic types: the centralized terminal units and the modular terminal units. The centralized terminal units are those which are useful to the conditioning of rooms of larger volume than the rooms which can be conditioned by a modular terminal unit. The centralized terminal units require in fact a network of air distributing conduits and air outlets for flowing into the room. The modular terminal units on the contrary are more complex, as they comprise in a single assembly the usual deadening devices, flow control devices and the conditioned air outlet nozzles.
In these cases such terminal units are connected to the centralized system by feeding pipes from which they receive conveniently filtered, heated or cooled, humidified or dehumidified air. Such systems are at present of two basic types, namely systems known as "all-air" systems and mixed "air-water" systems. The difference between the two types of system stands in the fact that with the mixed type systems there are provided in the room to be conditioned air treatment units comprising heat-exchangers through which heated or cooled water flows, such as to cause water sensible heat to be transmitted to or subtracted from the conditioned room.
The terminal unit according to the present invention, may be applied to both the above-mentioned types of system and in particular it is a variable flow modular-type terminal unit, thus being sufficient by itself only to provide to the conditioning of a room. As it is known, such conditioning is a function of a number of parameters, among which the type of room to be conditioned is mainly important. As a matter of fact there are peripheric and central rooms. Peripheric rooms are considered those in contact with the outside through the building outside main walls and the ceiling, thus having temperature and humidity influenced not only by internal variations, but also by modification of the external climate. Central rooms are considered those which are only influenced by internal thermic weight variations, caused by the persons in the room, lighting, electromechanical apparatus, etc. In both cases the thermic weight is always extremely variable, either when heat has to be brought or removed in order to keep constant the room temperature.
This purpose is achieved, in the known terminal units, by varying the flow quantity of conditioned air fed into the room, according to the temperature variations, whereby it is provided to modify the passage cross-section of the conditioned air in a zome upstream of the air outlet, the cross-section of which cannot be varied. With terminal units of this type the conditioning is satisfactory only for flow quantitites being the maximum flow or very near to the maximum, whereas it becomes quickly unsatisfactory when, due to a flow reduction, a consequent reduction of air outflow speed occurs. In order to obviate this drawback it has been designed to utilize the so-called "wall" effect, i.e. the phenomenon according to which, upon blowing air parallel to the horizontal surface of a ceiling, air itself stays for some time near the ceiling. A first drawback of this solution is due to the fact that, if air entering the room has a lower temperature, the density difference causes air to descend and, below a certain value of inflow speed, the layer of air, temporarily adhering to the ceiling, runs downwards giving rise to dangerous and annoying cool downdraughts. Air flow given by such units is therefore seldom less than 50% of the maximum flow.
Another drawback of such solution results from the fact that, if the temperature of entering air is higher than room temperature, a flow reduction and therefore a speed reduction causes an emphasizdd stagnation phenomenon with sensible temperature differences at the various heights in the room and upwards increasing temperatures. Sometimes, in the same room, differences of 5.degree. -6.degree. C may occur, from the ceiling to about half height of the room. In addition, at the ceiling there are provided room air intake devices. It is clear that such devices cause air at the highest temperature in the room to be sucked, with consequent loss of thermic energy. A further drawback shown by the known terminal units results from the fact that, to utilize at the most the above mentioned "wall" effect, it is necessary to provide a false ceiling, the lower surface of which, facing to the room, is positioned flush with the terminal unit outlet. This renders more complicated the manufacture of room ceilings and in addition more difficult the routine maintenance of the conditioning systems as, for the access to the terminal units, it is necessary to remove the false ceiling. Furthermore the latter must be completely smooth, without projections, since a protruding part would cause air flow to be diverted downwards thus giving rise to out-of-control air streams, which would affect the thermic conditions within the room, thus rendering extremely difficult a correct control of the conditioning.
A further drawback shown by the known terminal units is that resulting from the delay with which such units respond to abrupt pressure variations of the fed air in consequence of flow reductions of other terminal units situated in other rooms. The thermostat usually provided in such units has in fact a time of intervention that may be exceedingly long, during which the room temeperature greatly differs from a predetermined value.
Still another drawback shown by the known terminal units derives from the considerable maintenance required upon installation for setting and regulation operations, with a need for a frequent employment of specialized operators.
Yeat a further drawback of the known terminal units is that of having, at every operational condition, an induction ratio with respect to room air which is sufficient to utilize conditioned air with temperatures substantially different from room air and therefore to increase the necessary volume of conditioned air.